The invention relates to a process for the preparation of methyl cyclohexyl-propionate in the presence of a ruthenium and/or palladium catalyst starting with methylcinnamate.
C. R. Hebd. Seances Acad. Sci. 1913, 156, 751 to 753 describes the hydrogenation of methyl cinnamate to give methyl cyclohexyl-propionate under Raney nickel catalyst at 170 to 185xc2x0 C. Increasing the temperature to 200xc2x0 C. results in ester cleavage and deactivation of the Raney nickel catalyst. The methyl cyclohexyl-propionate produced using the process has insufficient purity.
The object of the present invention was to prepare methyl cyclohexyl-propionate in high purity.
We have found a process for the preparation of methyl cyclohexyl-propionate by hydrogenation of methyl cinnamate in the presence of a catalyst, which is characterized in that a ruthenium and/or palladium catalyst is used.
Ruthenium and palladium catalysts are known per se (Methoden der organischen Chemie [Methods in Organic Chemistry]/Houben Weyl, Volume IV/1c, Reduction Part 1, Georg Thieme Verlag, Stuttgart, 1980, pages 15 to 562, Handbook of Heterogeneous Catalysis, Vol. 1-5, pages 2123 to 2447; V C H Weinheim; 1997).
The catalysts are usually applied to a support. Examples of suitable supports are activated carbon, silicon dioxide, calcium carbonate, and aluminum oxide. The preferred support is activated carbon.
The support for the process according to the present invention generally comprises from 1 to 20% by weight, preferably from 5 to 10% by weight, of ruthenium and/or palladium, based on the overall catalyst.
It is also possible to use mixed catalysts of ruthenium and palladium.
For the process according to the present invention, the catalyst can be used in the dry or moist state (up to 60% of water).
For the process according to the present invention, the weight ratio of the catalyst used to methyl cinnamate is from 0.0001:1 to 0.1:1, preferably from 0.005:1 to 0.05:1.
The reaction temperature for the process according to the present invention is from 30 to 250xc2x0 C., preferably 60 to 200xc2x0 C.
The hydrogen pressure is from 1 to 100 bar, preferably from 10 to 20 bar.
The reaction time is from 2 to 100 hours, preferably 5 to 40 hours.
The process according to the present invention can be represented by the following reaction equation: 
The process according to the present invention is generally carried out as follows:
The pressure container fitted with stirrer is charged with the methyl cinnamate and the catalyst. Hydrogenation is carried out at the chosen reaction temperature and hydrogen pressure. The resulting methyl cyclohexyl-propionate is obtained following removal of the catalyst by filtration, decantation or centrifugation.
In the process according to the present invention, methyl cyclohexyl-propionate is produced in a purity of  greater than 99.5% and a yield of about 99%.
Methyl cyclohexyl-propionate is a fragrance having a fruity character, which is simultaneously also a starting material for the preparation of allyl cyclohexyl-propionate. Allyl cyclohexylpropionate is a fragrance with a strong pineapple odor (S. Arctander, Perfume and Flavor Chemicals, No. 77, 1969).
Methyl cinnamate for the process according to the present invention can be prepared by esterification of cinnamic acid with methanol or by Claisen condensation of benz-aldehyde and methyl acetate (K. Bauer, D. Garbe, Fragrance and Flavor Materials, page 80, Weinheim, V C H Verlagsgesellschaft, 1985).